EP2655502A1

EP2655502A1 - Composite of polymeric material with mineral fillers

Info

Publication number: EP2655502A1
Application number: EP20110811007
Authority: EP
Inventors: Anti VIIKNA; Andres KRUMME; Anneli REINOK; Rein KUUSIK; Tiit KALJUVEE
Original assignee: Tallinn University of Technology
Current assignee: Tallinn University of Technology
Priority date: 2010-12-23
Filing date: 2011-12-22
Publication date: 2013-10-30
Also published as: EE05628B1; EE201000091A; WO2012083972A1

Abstract

The present invention relates to the composite of a polymeric material with mineral fillers, which can be used for producing films, pipes and other products made by extrusion or injection moulding methods. The composite contains a homogeneous mixture of mineral and organic additives and thermoplastic polymers, whereas industrial waste, such as oil shale fly ash or clinker dust of cement industry or limestone mud or a mixture of the named substances, is used as mineral filler.

Description

COMPOSITE OF POLYMERIC MATERIAL WITH MINERAL FILLERS

TECHNICAL FIELD

The invention relates to the composite of a polymeric material with mineral fillers which can be used for making films, pipes and other products produced by extrusion and injection moulding methods. The invention is aimed at utilizing less known mineral fillers like oil shale fly ash, clinker dust from the cement manufacture and mud from limestone industry in composites of a thermoplastic polymer. In the context of this invention the term ..composite of thermoplastic polymer with mineral fillers" means a solid, e.g. one with its thickness negligible compared to its length and width (a film) or a three-dimensional solid (product) consisting of a homogeneous mixture of additives (e.g. mineral and organic) and a thermoplastic polymer. The thermoplastic polymer is usually a thermoplastic polyolefin (e.g. polyethylene, polypropylene) of first use or a reused polymeric material (polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyethylene terephtalate etc).

BACKGROUND ART

One of the most used raw materials for blown and extruded films and other products manufactured in a similar way, such as pipes, containers, boxes, consumer goods etc is polyethylene, but also polypropylene, which gives to the films and three-dimensional products the needed physical properties. In order to control the physical properties of films, nowadays chalk powder is used in most cases. Adding chalk as filler in a thermoplastic melt changes its melt flow index in the desired direction. Chalk powder is widely used in several industries, e.g. paper industry, where it is important to maintain its high quality, purity, whiteness, which in its turn enhances its price. In films, especially in dark-coloured ones, based on reused thermoplastic materials, whiteness is not required. Instead, the flow properties of the yielding composite and reduced prime cost are important. Therefore, the present invention offers a novel solution to substitute chalk powder with cheap fly ash originating from oil shale combustion in furnaces, clinker dust from cement industry, limestone mud or a mixture of these. Most of ashes arising from oil shale combustion are bottom ashes, which are removed from the furnace. These ashes cannot be used for the composite of this invention, they are deposited in landscape.

Oil shale fly ash is volatile and emanates from the combustion zone together with smoke gases. It is gathered from the electrical filters installed into the smoke removal systems of furnaces. Most of the particles (85-95%) are very fine (< 45 pm). Main phases of oil shale fly ashes are quartz, thermo-transformed clay minerals and secondary silicates. Fly ashes differ from bottom ashes in their lower content of calcite and lime, as well as smoother surface and spherical shape of particles. Clinker dust from cement production is largely similar to oil shale fly ashes in terms of chemical and phase composition, as well as dimensions, shape and surface structure of particles. Mud from the manufacture of limestone is also fine-grained - more than 90% of the particles are < 45 pm. Calcite, quartz and clay minerals dominate in the composition. Background of the invention includes solutions where coal fly ash is used as mineral filler, for example, in Chinese patent applications CN 0142931 OA, CN101358008A or in report„Fly ash/plastic synthetic aggregate for construction material" Swan C.W, et al, 2002, Chelsea Center for Recycling and Economic Development Technical Research Program etc. it is often called just fly ash, without specifying its origin. However due to the different physical and mechanical characteristics of coal fly ash compared to oil shale fly ash, such specification is necessary. Coal fly ash is solid powder which emanates together with smoke gases of the furnace during combustion of coal and which is entrapped by electric filters or filter bags. Particles of fly ash have dimensions from 0.5 to 100 pm. They mostly consist of silicon dioxide, aluminium oxide, iron oxide, they are of heterogeneous composition, the glass-like and the crystalline phases are present. One of the main disadvantages of coal fly ash is the considerable content of toxic substances in it, such as arsenic (43.4 ppm), barium (806 ppm), beryllium (5 ppm), boron (311 ppm), cadmium (3.4 ppm), selenium (7.7 ppm), strontium (775 ppm) etc. Oil shale fly ash considerably differs from coal fly ash both in its chemical composition and colour. Due to the high content of residual coke in it, coal fly ash is dark grey and polyolefin film made with it is dark grey to black. The advantage of oil shale fly ash is that the mentioned toxic components and residual coke are practically missing in it and its colour is light brown. This enables one to produce light-coloured film and other products, which can be further coloured by means of pigments.

Due to the fact that the current invention describes use of mineral fillers like oil shale fly ash, clinker dust and limestone mud in polymeric composites, the mentioned use will be compared only to published so far inventions related to composite films and other products with mineral fillers and their production.

In patent application CN10142931 OA, production of a composite material from used plastics is described, with addition of fly ash from combustion of coal. To these ends, reused plastics (polyethylene, polystyrene, polyvinyl chloride) and coal fly ash are mixed in certain proportions/ratios. Boards that could be used for building purposes are made by hot pressing.

Unlike the extrusion method in the current invention, the method used in the above patent application is hot pressing, which does not yield the properties of products described in the current invention. In patent application CN101358008A a special material is described for making buried polyethylene drainage pipes. For this, modified fly ash, heavy calcium carbonate and crystal whiskers are mixed in a high-speed mixing machine until uniformly dispersed powder is obtained. The powder is then mixed with polyethylene and the yielding mixture is fed to the extruder to make the special material, characterized by long service life, strong resistance to corrosion and low cost.

The ideas described in the above-mentioned patent application differ from the current invention because coal fly ash is used in a premixed powder, which is fed directly to the extruder. In patent application CN101376577A, production of a building material is described in which plastic is mixed with solid waste material. The plastic contains 30-60% of polyethylene, polypropylene, polyvinyl chloride, polystyrene and/or polyethylene terephtalate. The solid mineral waste material is coal fly ash, furnace slag and/or dust from building materials industry. The raw materials are uniformly mixed and necessary building blocks are press formed.

The procedure described in the above patent application differs from the current invention because it uses coal fly ash, furnace slag, dust from building materials industry, in addition to polyolefins together with polyvinyl chloride or polystyrene and polyethylene terephtalate, by method of press forming

Article „Thermal and rheological behavior of ultrafine fly ash filled LDPE composites" Hashmi, S. A. R, from Journal of Applied Polymer Science (2008), 107(4), 2196-2202 investigates blending of fly ash and low density polyethylene, as well as melt and flow properties of the obtained specimens. The procedure described in the article differs from the current invention because it deals with blending of coal fly ash with low density polyethylene, melting and rheological tests of the yielding composite material.

Article„Novel fly ash filled polypropylene master batches and its application on polyolefins" Patel, J. B, Patel, M. R. from Popular Plastics & Packaging (2007), 52(1), 96-100 describes use of fly ash in blends with low density polyethylene, high density polyethylene and polypropylene, physical properties of prepared specimens were measured.

The procedure described in the article differs from the current invention because it describes investigation of physical properties of specimens of a composite material obtained by blending coal fly ash with low density polyethylene, high density polyethylene and/or polypropylene.

Article "Preparations of filling masterbatch from oil shale ash for molding plastics and rubbers", By Xiao, Qihai from Zhongguo Suliao (2000), 14(10), 48-53 describes physical-mechanical and rheological properties of basic blend pellets made with oil shale fly ash compared to calcium carbonate filled basic blend. The basic blend under investigation was found to have better aging and flow properties.

The content of the article differs from the current invention because it compares properties of specimens of a basic blend made of pellets of a composite material made on the basis of fly ash of a particular Chinese kind of oil shale to specimens made with chalk filler.

Patent CN1042545C (CN1098117A) describes oil shale ash as filler in polyolefins and making composites of it. The named composites contain titanates (0.5-1.2 % of oil shale ash content), disperser (stearic acid, 1-3% of oil shale ash content), lubricants (waxes, 10-15% of oil shale ash content) and low density polyethylene (10-15% of oil shale ash content). The named patent differs from the current invention because oil shale ash is used, the physical and mechanical characteristics of which are different compared to oil shale fly ash as described above. In summary, the descriptions which might be possible prototypes of the present invention differ from the present invention because:

- they describe use of coal fly ash instead of oil shale fly ash;

- the described technologies do not use clinker dust or limestone mud;

- properties of composites with oil shale fly ash are described, but there is no indication of their applications in technology.

DISCLOSURE OF INVENTION

The aim of the current invention is to propose substitution of chalk powder in films, especially those based on dark-coloured reused thermoplastic materials, so that rheological properties of the yielding composite are maintained and, at the same time, its production cost will decline. Further to that, the aim of the invention is to create a composite material with mineral filler (made of industrial waste beforehand). The aim of the invention is reached by making a composite from a thermoplastic polymeric material and industrial waste, the filler being oil shale fly ash, clinker dust or mud from limestone processing industry or a mixture of these.

Polyolefins like polyethylene and polypropylene or polyvinyl chloride or reused polymeric material like polyethylene, polypropylene, polyethylene terephtalate or polyvinyl chloride are primarily used as the polymeric thermoplastic material.

Content of filler in the polymeric thermoplastic material, such as oil shale fly ash or clinker dust or mud from limestone processing industry or mixture of these, varies from 2 to 70 mass per cent. At that, the composite may comprise:

- oil shale fly ash: 0 to 70 mass per cent,

- clinker dust from cement industry: 0 to 70 mass per cent,

- limestone mud: 0 to 70 mass per cent or

- a mixture of these altogether 2 to 70 mass per cent.

As one option, the composite may comprise, in addition, 2 to 10 mass per cent of copolymer of ethylene with maleic anhydride and/or copolymer of ethylene and acrylic acid.

As another option, the mineral filler (oil shale fly ash or cement clinker dust or limestone mud or a mixture of these) in the composite may be treated in advance with 1 to 3 mass per cent of amino ethyl amino propyl trimetoxysilane, paraffin, wax, 0.5 to 3 mass per cent water solution of polyvinyl alcohol or 1 to 3 mass per cent water solution of quarternary ammonium salts.

Yet another option is to add in advance 1 to 5 mass per cent of paraffin to oil shale fly ash or cement clinker dust or limestone mud or a mixture of these, for plasticization purposes.

As one more option, the oil shale fly ash or clinker dust or limestone mud or a mixture of these in the polyolefinic composite may be mixed in advance with 30 to 98 mass per cent of powder of linear low density polyethylene, yielding improved flow properties of the blend. Diameter of the particles of the mineral filler in the composite is 5 to 50 μιτι, preferably 10 to 40 pm.

Manufacturing of film according to the invention is done in an extruder working by film blowing method or extruder with flat die. It is advisable to use first a twin-screw extruder (i.e. compounder) in order to uniformly add fillers and other substances to the reused polymeric material and to mix these. Of the yielding blend, pellets or other suitable forms of material are made, which are used thereafter for manufacturing film by extrusion, extrusion blowing or flat die method, or other products by injection moulding. Film is made in a device where the molten mass of the film composite leaving the extruder is directed into the annular die, and the sleeve issuing from there is cooled with air both from inside and outside. The inner airflow is under slight overpressure, making the sleeve to expand to the foreseen width. This enables one to control the thickness of the film at once. The sleeve is stretched lengthwise at the same time. The film made in this way is called blown film. The issuing film is wound round small rolls. By controlling the speed of the rolls, the film is stretched at the same time. While being stretched, the film usually decreases in thickness. The film may also be made in a flat die device.

In order to make products by injection moulding, first, pellets are made of the polymeric substance, mineral filler and additives by means of a granulator. The pellets are then fed into the extruder. Industrial machines may be used - a screw revolving and shifting in heater bodies pushes the composite melt towards the nozzle. The nozzle having contacted the mould, the mould is filled with the composite melt under pressure. The process is cyclic. The filled mould is cooled, opened and the formed product is removed. As an alternative, the mould may be substituted by dies of various shapes. The melt passing through these dies acquires the shape of a constantly forming profile - pipes, laths, rods of various shapes and diameters. The profile of these products is determined by the shape and dimensions of the die. BEST MODE FOR CARRYING OUT THE INVENTION

Polymeric composite with mineral fillers, according to the current invention, used for making film or three-dimensional products, consists of a homogeneous blend of mineral and organic additives and thermoplastic polymers, whereas the mineral filler in the composite is mostly industrial waste - oil shale fly ash or dust of cement clinker or limestone mud or a mixture of these in the following proportions:

- thermoplastic polymeric material 30 to 98 mass per cent.

- oil shale fly ash or dust of cement clinker or limestone mud or a mixture of these 2 to 70 mass per cent. Example 1 : Composite film containing LDPE and oil shale fly ash

Low density unused polyethylene (LDPE - low density polyethylene) was mixed in a drum mixer with oil shale fly ash (e.g. 25 mass per cent, particle diameter 10-40 Mm). The obtained mixture was poured into the hopper of the extruder and was mixed in its turn in the film line extruder at a die temperature of 190°C and a screw rotation frequency of 24 to 38 rpm. Extruder Reifenhauser S45 was used, with a heated annular die of a diameter of 80 mm and gap of 1 mm. Diameter of the screw of the extruder was 45 mm and length 5D. In order to manufacture a bi- axially oriented film by extrusion blowing, the extruded sleeve was directed upwards, stretched and blown simultaneously from inside. The cooled sleeve was pressed between the rolls and wound onto the spool. The formed film composite is a matrix where the oil shale fly ash addition is dispersed as small particles.

Example 2: Composite film comprising 2 to 70 mass per cent oil shale fly ash or cement clinker dust or limestone mud or a mixture of these.

In order to obtain regranulated polyethylene composite film a predetermined quantity of oil shale fly ash or cement clinker dust or limestone mud or a mixture of these was used, the dimensions of the particles of which were 10-40 pm, it was modified with water solution of aminoethyl aminopropyl trimetoxysilane or 2% water solution of ammonium salts or 1% solution of polyvinyl alcohol. The yielding powder was dried in a ventilated drying chamber at 105 °C up to moisture content of 2%. The silanized mineral filler was mixed in a drum mixer with pellets of regranulated polyethylene. The resulting dry mechanical mixture was poured into the hopper of the twin-screw compounder Brabender and was compounded at 190 to 200 °C and 30 to 40 screw rotations per minute. The rod-like material leaving the die was cooled and cut into pellets. Composite film was manufactured of these pellets by extrusion blowing as described in Example 1.

Example 3: Hot pressed specimen comprising 2 to 70 mass per cent of oil shale fly ash or cement clinker dust or limestone mud.

In order to make a moulded specimen, polypropylene and a predetermined amount of silanized oil shale fly ash or cement clinker dust or limestone mud was used, with particle dimensions 10 to 40 pm, e.g. by compounding as described in Example 2. The obtained pellets were poured into the hopper of injection moulding device Battenfeld BA 230/45. Specimens for mechanical testing were formed by injection moulding.

Claims

1. A composite of a polymeric material with mineral fillers comprising a homogeneous mixture of mineral and organic additives and thermoplastic polymers, whereas the composite comprises as mineral fillers mainly industrial waste, whereas the industrial waste used as filler is oil shale fly ash or cement clinker dust or limestone mud or a mixture of these in the following proportion:

- thermoplastic polymeric material 30 to 98 mass per cent

- oil shale fly ash or cement clinker dust or limestone mud or a mixture of these 2 to 70 mass per cent.

2. The composite of a polymeric material with mineral fillers according to claim 1 , whereas particle size of the mineral filler is from 5 to 50 pm, preferably 10 to 40 pm.

3. The composite of a thermoplastic material with mineral fillers according to claim

1 or 2, whereas the composite comprises, in addition, 2 to 10 mass per cent of copolymer of ethylene with maleic anhydride and/or copolymer of ethylene with acrylic acid.

4. The composite of a polymeric material with mineral fillers according to claim 1 ,

2 or 3, whereas oil shale fly ash or cement clinker dust or limestone mud or a mixture of these is treated in advance with 1 to 3 mass per cent water solution of aminoethyl aminopropyl trimetoxysilane.

5. The composite of a polymeric material with mineral fillers according to claim 1 , 2 or 3, whereas oil shale fly ash or cement clinker dust or limestone mud or a mixture of these is treated in advance with 0.5 to 3 mass per cent water solution of polyvinyl alcohol.

6. The composite of a polymeric material with mineral fillers according to claim 1 , 2 or 3, whereas oil shale fly ash or cement clinker dust or limestone mud or a mixture of these is treated in advance with 1 to 3 mass per cent water solution of quarternary ammonium salts.

7. The composite of a polymeric material with mineral fillers according to one of the claims 1 to 6, whereas oil shale fly ash or cement clinker dust or limestone mud or a mixture of these is mixed in advance with 30 to 98 mass per cent of polyethylene powder.

8. The composite of a polymeric material with mineral fillers according to one of the claims 1 to 7, whereas 1 to 5 mass per cent of paraffin is added in advance to oil shale fly ash or cement clinker dust or limestone mud or a mixture of these.